Rock Topics

Extrusive and Intrusive (Part 2)

Extrusive Rocks (Continued)

Pyroclastic rocks form from the lithification of broken fragments of rock from volcanic eruptions.

BrecciaPyroclastic texture in a volcanic breccia (Photograph by Parvinder Sethi)

This rock is made up of broken pieces of volcanic material.  It is called a volcanic breccia, and is a type of extrusive igneous rock.

Flood basalts are very large lava flows that come from large fissures or cracks in the earth. 

Columnar basaltCatoctin Formation, an ancient flood basalt in Virginia (Photograph by Stan Johnson)

The Catoctin Formation, shown here along the  Blue Ridge Parkway, is an ancient flood basalt.  This basalt flowed over large parts of Virginia about 570 million years ago.